Tooth bioengineering is of great interest, because dental decay and tooth loss constitute an important public health issue. Additionally, tooth anomalies are common in many craniofacial syndromes, and the easy accessibility of the oral cavity makes teeth an excellent test case for organ replacement. A thorough understanding of the molecular processes that drive tooth formation will be crucial to efforts to build new teeth. We are using the mouse incisor as a model for understanding the mechanisms that underlie the ability of stem cells to contribute to renewal of dental tissues, because it grows continuously due to the presence of adult stem cells. In this application we propose to learn about the natural role of RNAi in regulation of stem cell-driven tooth renewal by focusing on how endogenous small RNAi molecules called microRNAs (miRNAs) control continuous growth of the incisor. We will determine the spatial expression pattern of miRNAs in incisor stem cells and their progeny, ascertain the effects of miRNA knockdown on self-renewal and differentiation in cultured incisor stem cells, and determine the effects of in vivo miRNA knockdown on incisor continuous growth. Together, these experiments will open a portal into a previously unexplored area: the endogenous, natural role of RNAi in stem cell-based tooth regeneration. The knowledge we gain will inform therapeutic approaches that aim to manipulate molecular pathways in order to enhance tooth repair or regeneration. PUBLIC HEALTH RELEVANCE: Tooth bioengineering is of great interest, because dental decay and tooth loss constitute an important public health issue. A thorough understanding of the molecular processes that drive tooth formation will be crucial to efforts to build new teeth. We propose to learn about the natural role of RNA interference (RNAi) in regulation of stem cell-driven tooth renewal by focusing on how endogenous small RNAi molecules called microRNAs regulate this process.